To download the SG3525 library for Proteus, follow these steps:

Extract the downloaded folder using a program like WinRAR or 7-Zip.

The recommended way to import is through the Proteus user interface:

C:\Program Data\Labcenter Electronics\Proteus 8 Professional\Data\LIBRARY (Note: "ProgramData" is a hidden folder by default in Windows. You may need to click "View" in your File Explorer tabs and check the box for "Hidden items" to see it.)